You can find the full source code for this website in the Seam package in the directory /examples/wiki. It is licensed under the LGPL.
Not currently. The problem is that Seam maintains references (such as the application scope map) that are supposed to be singular, yet end up getting shared across modules because of the storage mechanism selected (for instances a static field). This causes interference between multiple WAR modules.
Effort is underway to fix Seam so that it properly isolates these references between individual WAR modules. Follow JBSEAM-3119 and JBSEAM-2523 for details. The issue reports contains a set of patches that are currently under review. The following mailinglist threads also provide information about the problem and the proposed solutions:
A solution is expected in one of the 2.2 releases of Seam, but if it turns out to be too challenging it will be deferred to Seam 3, which will be designed for this scenario from the start.